Magnesium ions inhibit the antigen-presenting function of human epidermal Langerhans cells in vivo and in vitro, involvement of ATPase, HLA-DR, B7 molecules, and cytokines

The combination of seawater baths and solar radiation at the Dead Sea is kn own as an effective treatment for patients with psoriasis and atopic dermat itis. Dead Sea water is particularly rich in magnesium ions. In this study we wished to determine the effects of magnesium ions on the capacity of hum an epidermal Langerhans cells to stimulate the proliferation of alloreactiv e T cells. Twelve subjects were exposed on four subsequent days on the vola r aspects of their forearms to 5% MgCl2, 5% NaCl, ultraviolet B (1 minimal erythemal dose), MgCl2 + ultraviolet B, and NaCl + ultraviolet B, Epidermal sheets were prepared from punch biopsies and were stained for ATPase and H LA-DR. Compared with untreated skin, the number of ATPase(+)/HLA-DR+ Langer hans cells was significantly reduced after treatment with MgCl2 (p = 0.0063 ) or ultraviolet B (p = 0.0005), but not after NaCl (p = 0.7744). We next q uestioned whether this reduced expression of ATPase and HLA-DR on Langerhan s cells bears a functional relevance. Six subjects were treated on four sub sequent days with 5% MgCl2, ultraviolet B (1 minimal erythemal dose), and M gCl2 + ultraviolet B, Epidermal cell suspensions from treated and untreated skin were assessed for their antigen-presenting capacity in a mixed epider mal lymphocyte reaction with allogeneic naive resting T cells as responder cells. Treatment with MgCl2, similarly to ultraviolet B, significantly redu ced the capacity of epidermal cells to activate allogeneic T cells (p = 0.0 356). Magnesium ions also suppressed Langerhans cells function when added t o epidermal cell suspensions in vitro. The reduced antigen-presenting capac ity of Langerhans cells after treatment with MgCl2 was associated with a re duced expression by Langerhans cells of HLA-DR and costimulatory B7 molecul es, and with a suppression of the constitutive tumor necrosis factor-alpha production by epidermal cells in vitro. These findings demonstrate that mag nesium ions specifically inhibit the antigen-presenting capacity of Langerh ans cells and may thus contribute to the efficacy of Dead Sea water in the treatment of inflammatory skin diseases.